There is a wide variety of peptides in blood. These peptides include peptides that indicate the differences in concentrations in blood between a living body with healthy and specific pathologic condition. Such peptides are useful as biomarkers for diseases in clinical test fields.
A protein such as albumin or globulin is contained in the blood (hereinafter also referred to as “protein in blood”). Peptides bind to the protein in blood in many cases. Therefore, in detection of peptides, it is preferable to liberate the peptides from the protein in blood. As a technique of liberating a peptide, there is a technique in US Patent Application Publication No. 2012/0277407, which is herein incorporated by reference. The method described in US Patent Application Publication No. 2012/0277407 is a method comprising heat-treating a solution containing a complex of peptide and albumin to form a non-peptide binding self-aggregate of albumin and liberating the peptide from the albumin.